In the field of inhalation therapy, it is generally desirable to employ therapeutic molecules having a particle size (i.e., diameter) in the range of 1 to 10 μm. Carrier molecules or excipients, such as lactose, for inhaled therapeutic preparations also include significantly larger diameter particles (e.g., 100 to 150 μm) that typically do not penetrate into the upper respiratory tract to the same degree as the active ingredient. In general, it is preferable to use a smaller particle size for the lactose or a lactose blend having a defined ratio of coarse and fine lactose.
The lactose particle size and distribution will also, in many instances, significantly influence pharmaceutical and biological properties, such as, for example, bioavailablity. For example, it is well known that coarse lactose in crystalline form has a fair flow rate and good physical stability whereas fine lactose powder, such as that produced by conventional fine grinding or milling, generally lacks good flow properties. Lactose prepared by conventional spray drying either lacks desired flow properties or contains too many large sized lactose crystals.
It is well known that one particular drawback associated with conventional means of producing pharmaceutical grade lactose relates to undesirable variations in particle size, morphology and distribution. Such production methods are particularly problematic in that they often lead to excessive and undesirable variations in the fine particle mass (“FPMass”) of pharmaceutical formulations employing such lactose. FPMass is the weight of medicament within a given dose that reaches the desired size airways to be effective. For example, a desired size may be defined as approximately 1 micron to 10 microns as measured by laser scattering techniques.
Lactose morphology is believed to be another important parameter to control, and it is believed that the degree of surface roughness can influence the interaction between the lactose particle and excipient and as such is now often measured as part of the lactose selection criteria. See e.g., Pharmaceutical Technology Europe April 2004, page 23.
It is possible that two lactose particles may be measured as having the same particle size, but if one is smooth, eg un-milled crystalline lactose, and the other is a rougher-surfaced milled crystal, that these could associate to a different extent with the active and thus impact upon either the initial FPMass performance or the through life stability performance of the product.